Circuit for applying ionizing pulses and boosted alternating current to an arc discharge lamp



Aprll 21, 1970 s, C PEEK 3,508,112

CIRCUIT FOR APPLYING IONIZLNG PULSES AND BOOSTED ALTERNATING CURRENT TOAN ARC DISCHARGE LAMP Flled June 29, 1967 United States Patent U.S. Cl.315240 3 Claims ABSTRACT OF THE DISCLOSURE An electronic circuit havinga pulse generating circuit for applying ionizing pulses to a fluorescentlamp which draws discharge current from an alternating current supply,and a transformer connected to the supply for boosting the alternatingcurrent applied to the lamp.

Conventional fluorescent lamp starting and operating circuits havecomprised a ballast for applying a high starting voltage to the lamp toionize it and start discharge and for inductively limiting currentthrough the ionized lamp. Because of the Weight and bulk of the ballastand its high expense, heating and noise, control circuits have beenproposed which start and control the lamp discharge by variouselectronic switching circuits. Some of the advanced electronicallyvalved circuits comprise pulse generating or gating means forperiodically applying a voltage pulse to the lamp thereby ionizing thelamp sufficiently to support an arc discharge for a limited period,usually a half-cycle or less of the alternating current supply. Becausestandard lamps and operating circuits are designed for about 110 voltoperation at least, they may fail to operate properly if the alternatingcurrent supply voltages drop much below 110 volts. Unlike ballastcircuits which apply an ionizing voltage well above that required forcontinuous operation, ionizing pulse generation circuits limit theamount of ionization and the amplitude of the ionizing pulses and areadversely afiected by line voltage drops.

It is the object of the present invention to provide an electronicpulsing circuit of the type described above with means for insuring thatthe ionizing discharge voltage is adequate for continuous operation ofthe lamp.

According to the invention an arc discharge lamp operating circuitcomprises discharge terminals for connection to the lamp, powerterminals for connection to a supply of alternating current, a powercircuit connecting said power terminals to said discharge terminalsincluding means for applying periodic voltage pulses to said dischargeterminals thereby to support an arc discharge by ionization in the lampand to draw current from said alternating current supply, and atransformer having a primary connected between said power terminals anda secondary connected between one power terminal and one lamp terminal,said primary and secondary being connected such that current in saidprimary induces current in said secondary substantially in phase withthe supply current in said secondary.

For the purpose of illustration typical embodiments of the invention areshown in the accompanying drawing, in which FIG. 1 is a schematicdiagram of a fluorescent lamp operating circuit according to theinvention.

The operating circuit of FIG. 1 comprises discharge terminals 1 betweenwhich are connected two four foot HO lamps L which may be considered asa single lamp. Power for the lamps is supplied from 115 volt, 60 cyclealternating current terminals A and C. Power terminal A is connected toa lamp terminal I through an autotransformer primary T1 and secondary T2having a turns ratio 3,508,112 Patented Apr. 21, 1970 ICC of 1 to 10 andnegligible reactance. Power terminal C is connected to a lamp terminal Ithrough the secondary T4 of a core transformer having a primary T3. Thecore transformer has a turns ratio of 12 in the primary to l in thesecondary and is hence a stepdown transformer. The primary T3, beingconnected across the 120 volt power terminals A and C, induces about 10volts in the secondary in phase with line current in the secondary,thereby boosting the RMS value of voltage applied to the lamp. The coretransformer reactance is of negligible reactance, e.g. less than ohms,compared to a conventional ballast.

A voltage pulse discharging circuit includes a triac V1 (G.E. typeSC45B), a diac D1 (G.E. type 5T2), a primary voltage pulse storagecapacitor C1 (6 mircrofarad) a secondary storage capacitor C2 (0.33microfarad) and a coupling capacitor C3 (0.07 microfarad). The primarystorage capacitor C1 and triac T1 are connected in series between thepower terminals A and C through the autotransformer primary T1, so thatduring each half-cycle of alternating current the primary storagecapacitor C1 charges, through the triac T1. In the succeeding halfcyclethe voltage across the secondary capacitor C2 rises toward the breakdownvoltage of the diac D1. When this breakdown voltage is exceeded the diacD1 conducts allowing the secondary capacitor C2 to discharge to the gateelectrode g of the triac and trigger the triac into avalancheconduction. The primary capacitor then discharges through the triac andautotransformer primary and reverses its charge. The discharge voltageis stepped up by the 1 to 3 ratio of primary to secondary, and thestepped up voltage (eg 300 volts peak) is applied to the lampterminals 1. At this instant a limited number of ions are established inthe lamps L, and the lamps fully ignite and conduct line current forpart or all of the half-cycle. About when the line voltage passesthrough zero the arc tends to extinguish depending on the amplitude andduration of the ionizing pulse. If the line voltage drops, the amplitudeof the ionizing pulse will drop and the lamps may be insufficientlyionized to start discharge or to maintain discharge until the next pulseis applied. The lamps might therefore fail to ignite, extinguishintermittently or flicker objectionably.

According to the present invention the core transformer T3, T4 adds asmall increment of voltage to the ionizing pulse and to the open circuitvoltage applied to the lamps. With one to twelve turns ratio thetransformer adds an increment of one-twelfth the line voltage, about tenvolts, which is adequate to maintain the voltage for which the lamps andpulsing circuit are designed with expected drops of line voltage, andyet does not increase the ionizing pulse peak voltage so much as toexcessively ionize the lamp at or expectably above normal line voltage.The transformer T3, T4 thus substantially increases the reliability ofthe operating circuit.

While one desirable embodiment of the invention has herein beendisclosed by way of example, it is to be understood that the inventionis broadly inclusive of any and all modifications falling within theterms of the appended claims.

Iclaim:

1. An arc discharge lamp operating circuit comprising:

discharge terminals for connection to the lamp,

power terminals for connection to a supply of alternating current,

a power circuit connecting said power terminals to said dischargeterminals, and means outside said power circuit for storing and applyingperiodic voltage pulses to said discharge terminals superimposed on saidsupply current thereby to support an arc discharge by ionization in thelamp and to draw current from said alternating current supply, and

3 4 a transformer of negligible reactance having a primary ReferencesCit d connected across said power terminals and a secondary connectedbetween one power terminal and one UNITED STATES PATENTS lamp terminal,the windings of said primary and 3,414,768 12 1968 Peek 315--240secondary being connected in additive voltage phase, 2,944,163 7/ 1960Walsh 30788 whereby alternating supply current in said primary 53,129,380 4/1964 LiChOWSkY 32345 induces current in said secondarysubstantially in 3,346,874 10/1967 WE 3078 8.5 phase with and inincrease of the supply current in 3,310,687 1967 Howell 307-88.5

said secondary from said supply terminals. 2. A circuit according toclaim 1 wherein said trans JOHN HUOKERT Pnmary Exammer former has astep-down turns ratio. B. ESTRIN, Assistant Examiner 3. A circuitaccording to claim 1 wherein the secondary to primary turns ratio ofsaid transformer is a minor US Cl. X.R.

fraction. 315100, 289; 32324, 45

